Oxazolidines, particularly bis-oxazolidines, are well known as curing agents for polyurethanes. Particularly useful as curing agents are bis-oxazolidines which are linked by urethane groups, disclosed, for example, in U.S. Pat. No. 5,747,627, U.S. Pat. No. 5,189,176 and GB Patent Document No. 1 463 944.
A further class of oxazolidines are bis-oxazolidines which are linked by carbonato groups. Such bis-oxazolidines are disclosed, for example, in EP Patent Document No. 0 499 188 A1.
A further class of oxazolidines are bicyclic oxazolidines which are disclosed, for example, in U.S. Pat. No. 5,126,421, International Publication No. WO 96/08308 A1, International Publication No. WO 99/07762 A1 and GB Patent Document No. 1 292 455.
Polyoxazolidines in general, and particularly polyoxazolidines having urethane groups, however, tend to crystallize. This is very disadvantageous in view of storage, transport and application of these compounds. There have been several approaches to solve this problem. The use of solvents show disadvantages such as impairment of mechanical properties and release of solvents such as volatile organic compounds (VOC).
U.S. Pat. No. 5,189,176 suggests a non-crystallising bisoxazolidine having two urethane groups linked together by a hexamethylene group and having a hydrocarbon substituent with 5 to 8 carbon atoms attached to the carbon located between the oxygen and nitrogen atom of the oxazolidine ring. However, this very narrow group of chemical compounds is very restrictive in the choice of suitable properties of polyoxazolidines.